Decolorization of tallow



Dec. 9, 1952 H. J. PASSINO' ET AL 2,621,198

DECOLORIZATION OF TALLOW Filed Dec. 51, 1949 PROPANE .RECYCLE fi as 47 l7 REFINED 7 TALLOW 23 27 24 28 l I2 L42 33 34 CRUDE TALLOW H PROPANEW INVENTORS COLOR HERBERT J. PASSINO aomzs By OLIVER MORFIT ATTORNEYS Patented Dec. 9, 1952 DECOLORIZATION OF TALLOW Herbert J. Passino, Englewood, N. J., and Oliver Morfit, Hartsdale, N. Y., assignors to The M. W. Kellogg Company, Jersey City, N. J., a corporation of Delaware Application December 31, 1949, Serial No. 136,304

4 Claims.

This invention relates to an improved method for decolorizing tallow, or other fatty oils, by solvent fractionation with a low-boiling solvent, such as propane, at a temperature in the range near the critical temperature in which solubility decreases as temperature increases, i. e. in the paracritical range of temperature. More particularly, this invention relates to the control of a continuous countercurrent contacting zone in which an upflowing extract phase containing substantially all of the fat in solution is subjected to the reflux action of a denser, downfiowing, reflux liquid, said control being accomplished by varying the reflux flow rate to limit the oil content of the upfiowing extract phase within predetermined limits found to give the maximum throughput without impairing the color quality of the product. In the preferred form of the invention, the extract phase is flowed upwardly through a precipitating zone of increasing temperature to precipitate the least soluble oil components as reflux liquid; the extract phase continues to flow upwardly through a settling zone maintained at a temperature about the same as the maximum temperature of the precipitating zone so that product oil is not discolored by the entrainment of precipitated raflinate material. Preferably, reflux oil is collected from the settling zone and introduced into the precipitating zone at a rate Which is efficient to maintain the desired solvent to oil ratio as determined by sampling upfiowing extract phase as it leaves the precipitating zone to enter the settling zone.

This application is a continuation-in-part of Serial No. 693,322, filed in behalf of the same inventors on August 27, 1946.

Crude animal fats or tallows, such as beef tallow and the like, find considerable use in the manufacture of soaps. Tallows usually contain substantial percentages of fatty acids and triglycerides which are particularly suitable for the manufacture of soap. However, the crude tallow which is generally obtained from slaughter houses also contains considerable color bodies and oxidized fats which must be removed before the tallow is suitable for making soap. In the past, the.

crude tallow, which is sometimes referred to as inedible tallow, was first split into a glycerine fraction and a crude fatty acid fraction. The fatty acid fraction was then distilled to produce an overhead classified as distilled fatty acids, and a residue known as still bottoms. The still bottoms were then redistilled to obtain an overhead distillate which was recycled back to the original fatty acid fraction for redistillation in the first step. The bottom from this second distillation is called the final pitch bottoms and constitutes approximately 8 per cent of the original tallow. According to this method, there is an approximate 8 per cent loss in the final pitch bottoms which contains not only the original color bodies but also undesirable products caused by thermal polymerization during the two distillations.

According to the present invention, the various diiliculties encountered due to the distillation of fatty acids are overcome and at the same time the process is greatly simplified. The crude tallow (and the term tallow as used herein includes any animal fat resembling beef tallow), heated sufliciently to be in liquid form, is continuously charged to the middle region of a solvent extraction tower (or any longitudinally extended countercurrent contacting zone equivalent thereto) having a solvent inlet and rafiinate phase outlet near the lower end, an extract phase outlet at the upper end, and a charge inlet intermediate said ends.

The low boiling solvent described hereinatfer is charged to the solvent inlet at a rate which is usually about 10 to 20 times (by volume) the tallow charge rate. The solvent to tallow charge rate ratio may rise as high as 30, or, very rarely, a ratio of less than 10 may be employed.

Within the tower, the solvent and tallow mixes to form extract and ramnate phases, the extract phase flowing upwardly and the rafiinate phase flowing downwardly. The contents of the tower are heated by steam coils or other suitable means to obtain paracritical conditions which result in desired extract and raninate phase compositions as described hereinafter. the tallow goes into the extract phase and is recovered therefrom in a white or nearly white, purified form. However, darkly colored impurities tend to appear from time to time in the overhead extract product because of a tendency of the tower to accumulate a large mass of oil. The principal featiue of the present invention is a method for preventing the accumulation of this mass of oil or keeping it within limits to prevent the appearance of colored material in the product.

The solvent must not be chemically reactive with the oil under the conditions of the process; it is also necessary that the solvent be of low critical temperature, preferably below about 450 F.; such solvents are of substantially lower molecular weight than the fats treated, are usually less dense and boil at much lower temperatures. There is little or no degradation of the tallow by heat when such low-boiling solvents are em- About 98 per cent of ployed. The tallow must be soluble in the solvent in the so-called paracritical range, the paracritical range being a range of temperature near the critical temperature of the solvent in which the miscibility of the solvent and oil decreases with temperature increases; this range usually extends from about 100 F. below the critical temperature of the solvent to a temperature a few degrees above the critical temperature of the solvent, the latter temperature being, perhaps, the critical temperature of the solvent-fat mixture. While a few normally liquid solvents meet the requirements, those which are normally gaseous and are maintained in the liquid condition during the extraction process by the application of pressure are preferred since they are easier to separate from the extract fractions. Such preferred solvents include the low-boiling hydrocarbons such as low-boiling parafhn hydrocarbons, low-boiling olefin hydrocarbons and other solvents having relatively low critical temperatures such as dimethyl ether, dichlorodifiuoromethane, methyl chloride, ammonia, carbon dioxide, etc. or a mixture of solvents which behave in a paraoritical manner below about 450 F. The low-boiling hydrocarbons are advantageous because of their stability and non-reactivity with the oil. While normally liquid paraiiin hydrocarbons may be employed, the lower boiling normally gaseous paraffins are preferred for reasons given above. Among these, propane is desirable because of its low critical temperature; its high degree of miscibility with the oils normally treated at relatively low temperatures, and because of the low pressure required to maintain it in liquefied condition.

In the rare case, in which the solvent is actually of higher density than the oil treated (for example, dichlorodifiuoromethane) the tower must be inverted, but the same concepts apply.

The solvent extraction method of decolorizing tallow is effective primarily because the paracritical conditions can be adjusted to precipitate precisely a small fraction of colored material. But the precision with which this material is precipitated and separated is largely dependent on satisfactory separation of the precipitated colored raffinate material from the upfiowing extract phase. If droplets of colored raifinate ma terial accumulate in the upflowing extract phase or if the vertical distance allowed for the settling of the droplets is too small, undesirable coloring material will appear in the product. Furthermore, the precision of fractionation is dependent upon sufiicient countercurrent contacting of downfiowing heavy phase with upflowing light phase so that the two phases can come into a precise equilibrium with all the extract material dissolved out of the downfiowing rafiinate phase and all the raffinate material displaced from the upflowing light phase by temperature conditions and by the presence of extract material. The downflowing oil, which is precipitated by temperature gradient or otherwise separated from the extract phase after having once been dissolved therein is referred to as reflux liquid, because, although at first dissolved in the extract phase, it is precipitated at some higher point in the tower and, as it flows downwardly, tends to rectify the division of the extract and raihnate materials between the upflowing and downfiowing phases. The solvent characteristics and the rate of flow of the crude tallow are the principal determinants of the maximum tower temperature. If this temperature is too high, less far for easy and inexpensive correction.

4 soluble fractions of the tallow are precipitated from the extract phase in the top of the tower. This material flows down and redissolves in upflowing propane when it reaches cooler regions at a lower point in the tower. This fraction tends to continuously increase. It is continuously redissolved and reprecipitated, shuttling back and forth between the top and bottom of the tower and continuously accumulating more of this kind from the incoming crude tallow. As time goes by, a heavy oil phase with a percentage of propane which is low relative to the extract phase. begins to fill the tower because it is too soluble at the lower temperature to come out the raf finate' outlet but not soluble enough to pass the high temperature region in the upper part of the tower. The portion of the tower above this accumulated oil which continues to function as a a decolorizing zone soon becomes inadequate, and droplets of the accumulated oil, which contain a great deal of colored matter, begin to be car'- ried over into the extract phase. By the time this coloring matter appears in the extract phase at the top of the tower, matters have gone too Uufortunately, the tower is operatin most efficiently, i.e at the greatest throughout, when it is on the verge of accumulating oil or flooding." The problem is particularly aggravating in large commercial installations because of daily and sometimes hourly variations in the composition of the tallow charge. It is efficient and desirable to operate a commercial plant for several months without shut down. A typical commercial plant of this type actually requires three to four tank cars of t-allow per day. These tank cars are brought in from many different sources and the quality and composition of the tallow varies radically from car to car. For example, one car may have 25 per cent fatty acids and the next 30 per cent fatty acids, to say nothing of the fact that one may be relatively much dirtier than the other. As a result of these variations, the tower rarely has more than a few hours of equilibrium operation. No sooner does it adjust to one composition of material than it begins to receive material of a different composition from another tank car. Several hours may be required for adjusting to equilibrium conditions for the new charge. Or, indeed, a charge may again shift in composition without the tower ever having reached an equilibrium condition. For example, substantial variation in fatty acids result in a great variation in the solubility of the color materials. Some colored materials appear almost insoluble in propane but very soluble in fatty acids and have an intermediate solubility in a solvent mixture comprised of propane and fatty acids. If the percentage of fatty acids in the charge suddently increases, these color bodies suddenly become more soluble in the extract phase and it is necessary to increase the top tower temperature.

It is evident from the foregoing that it is desirable to have a means of controlling tower con ditions from hour to hour so that the tower can be operated at a maximum throughput without the accumulation of excess reflux liquid. The conventional practice of inspecting the color of the extract phase after it has been withdrawn from the tower is not satisfactory, since, by the time coloring material appears in the extract phase, the tower is so filled with dark colored reflux oil that several hours will be required before satisfactory operations can be resumed.

Moreover, it is necessary to reprocess several tons of inferior product. Also, the reduction in tower temperature or in refluxing which may correct the conditions on one day may prove to be an over compensation for the charge oil of different composition which comes in the following day.

The present invention meets these difficulties by providing the control method which is based not merely upon examination of color of extract phase samples from the uper end of the tower or from various other points of the tower, but upon the ratio of solvent to oil in the extract phase. Moreover, the control steps which are taken upon the basis of the analysis of the extract phase are not mere adjustments of tallow and propane supplied but, on the contrary, are directed primarily to control of the amount of reflux liquid which flows downwardly in the tower. The total reflux oil flowing downwardly at any predetermined control point within the tower is increased if the solvent to oil ratio of the sampled extract phase is too high and reduced if the solvent to oil ratio is too low. The invention is not limited as to the method by which this reflux liquid is increased or reduced; it may be done by varying the rate of externally introduced reflux or by varying the rate at which downfiowing oil is collected and withdrawn from some point within the tower, or by manipulating the temperature gradient. Finally, control is made more effective by provision of a special settling zone. All these features represent variations of the invention.

An apparatus for practicing the method of the invention in its preferred species is shown in the drawing. The process is carried out in a tower I0, typically about 60 ft. high and provided with an internal counterfiow bafiie structure. Crude tallow and propane are charged to the tower through a propane inlet II and crude tallow charge inlet 12, the latter usually being about 20 ft. above the bottom of the 60 ft. tower. Within tower l0, temperature conditions are controlled partly by preliminary heating of propane and tallow in heaters l3 and I4 and partly by heat exchanger l5, l6, l1 and Hi. It is apparent, of course, that other heating means might be resorted to in order to maintain the desired temperature conditions within the tower; for example, the reflux liquid or other material withdrawn from the tower 10 might be heated before recycling to the tower. The temperature conditions within the tower are adapted to d ssolve substantially all of the tallow in the propane but a small percentage of impurities, color bodies, oxidized fats, and the like are either insoluble in propane or so slightly soluble that they will precipitate into 1 to 4 per cent rafilnate phase to be withdrawn through railinate phase outlet l9 at the bottom of tower Hi. This raflinate phase is often so thick and gummy that it is desirable to agitate the rafiina-te phase material in the raifinate phase bottoms to prev nt it from clogging outlets and also to permit the incoming propane to thoroughly scavenge residual tallow in the rafiinate phase. Although this agitation might be carried out by means of a beater, the embodiment shows the employment of a simple agitation means in the form of recirculation of a percentage of the raflinate bottoms through line 20 by means of pump 2|. Further to assist in the scavenging of the tallow from the rafdnate phase, the interface between the raifinate phase and extract phase is maintained at a point some distance above the propane inlet as indicated by the dashed line 22. The upfiowing extract phase 6. formed in the lower region of tower [0 by the solution of tallow in propane contains not only all the desired tallow product but some of the more soluble impurities and some entrained insoluble impurities. As it passes upwardly, the length of the tower permits settling of the entrained material and a temperature gradient causes the precipitation of the soluble impurities. Nevertheless, if the tower is being operated at a high throughput rate, as it is economically desirable to do, some residual material remains in the upfiowing extract phase for a short period even after the maximum temperature is reached.

When the tower is first on stream, the small percentage of residual material presents no difficulty; but after a few hours of operation, the tower begins to accumulate a substantial quantity of this residual material. It is material which is almost as soluble as the desired tallow product and,

therefore, tends to dissolve in the upflowing extract phase in the region of tallow inlet I2, and

is only precipitated because of the temperature gradient. It is inevitable that under equilibrium conditions as maximum amount of this material will be constantly circulating within the tower,

being momentarily carried up in the extract phase, precipitated at the top and redissolved lower down. It is not merely the rates at which propane and tallow are charged to the tower which determine the color of the tallow product in the extract phase. Even after equilibrium conditions have been reached, it is not possible to maintain consistency of product merely by maintaining a constant temperature gradient.

,There are suirlcient variations in the tallow to make it necessary to adjust either continuously or periodically, ordinarily at periods of about 2-6 hours each. In the tower shown approximately 9000 lbs. per hour of tallow and 22,000 gals. per hour of propane are charged. A temperature gradient of 1 to 2 degrees near the bottom of the tower up to about 4 to 6 degrees near a collecting tray 23 is maintained. Above the collecting tray 23, the temperature is preferably maintained at its constant value near the maximum or only slightly below it. The region above collecting tray 23 serves as a settling zone in which oil droplets have a chance to separate from the upflowing extract and to flow downwardly and be accumulated in collecting tray 23. In the region of collecting tray 23 or slightly below it an inverted collector means 24 is provided for sampling upflowing extract phase. The samples are withdrawn through line 25 and accumulated in a suitable sample accumulator means 26. As frequently as the process seems to require, a sampleof extract phase is taken from accumulator means 25 and its weight and volume determined. An estimate of the solvent-oil ratio may be made from these figures and from the temperature and pressure cond tions. The solvent is then vaporized, the oil remainder weighed, and the gas volume measured. These latter figures form the basis for a more accurate determination of the solvent il ratio. The two methods of determining the solvent-oil ratio serve to check one another.

Downflowing oil accumulated in collector tray 23 is withdrawn through line 21 and diverted by means of three-way valve 28 either back to tower Hi through line 25! or withdrawn through line 33, to be discarded or stored, or reincorporated in the crude tallow feed. Valve 28 may be controlled continuously or merely adjusted periodically as indicated by solvent to oil ratio determinations of samples taken from accumulator means 28. If the oil content of the extract phase momentarily exceeds an allowable percentage, which will vary for: the degree of refining required, but will preferably not be in excessof 16 per cent, then oil collected in collector 23 will be diverted through line 30 instead of being returned. to tower I through line 2 9. If, on the other hand, the oil content of the upflowing' extract phase declines substantiallybelow the rangein. which suitable product oil is obtained, then all or a substantial portion of the oil collected in collector 23 will be returned to the tower through reflux line 29. Under some conditions, for example, if the velocity of the upfiowing extract phase is high in comparison with the height of the tower, it is desirable to control the rate of refluxing by samples taken from a point not far above tallow charge" inlet 12.. An inverted sampling means 32 is shown forwithdrawing'upflowing extract'phase in the lower portion. of the precipitating zone of tower I0. Samples of extract phase entrapped by collector means 32 are withdrawn through line 33 and accumulated in accumulator 34, solvent-oil ratio being determined as previously mentioned in connection with accumulator 26.

Upfi'owing' extract phase is withdrawn from the topof tower l0 through line 35 at a rate controlled by valve 36 which also serves to reduce pressure upon the extract phase so that when it is introduced into a lower pressure tank 3? at a pressure of say 300 pounds per square inch, a substantial part of the propane vaporizes and is withdrawn in gaseous form through line 38. A part of the partially desolventized. remainder may be returned to the upper portion of tower I'D-which may be designated as the settling zone through line 39 bymeans of pump 49. The bulk of the partially desolventized extract phase, however, will be withdrawn from line 4| and pressure reducing valve 42 to avessel 43 under a still lower pressure of pounds per square inch. In vessel 43 heat by means of the heating coil 44 may be applied in order to eliminate the remainder of the solvent. Refined tallow is withdrawn through valve 45. Vaporized solvent is withdrawn overhead through line 46, repressured in compressor 41 and together with the solvent vapor in line 38, is passed through condensers to astorage tank (neither of which is shown) for reuse in the process.

It is to be understood that other possible variations such as different gradients, pressures and temperatures fall within the scope of this process;

The sampling of upfiowing extract phase may be at one or more points in the tower above the charge inlet l2. The location shown is mere- 1y a preferred location.

Moreover, the term used in the claims, with drawing upflowing extract phase, includes either performing this operation continuously or merely from time to time, for example, every few hours.

It should be understood also that the location of the interface between the bottom and upper phase material at a point above the propane inlet as indicated in the drawing by numeral 22 is only a preferred location. In some cases it may be found desirable to operate the tower with the interface at a lower level than propane inlet ll.

Better settling may be accomplished in the settling zone region of tower I!) by constructing the upper portion of the tower with an increased horizontal cross-section in order to reduce the- 10 to 1, 20 to 1 or 50 to 1 or even higher. Not.

only is the decolorization more eflicient, but also larger quantities of substantially decolorized fatty material are obtained. For example, when a propane to fatty material ratio of approximately 10 to 1 is used, it may be necessary to remove 5 or 6 per cent of the crude fatty material as bottoms in order to obtain an overhead product having satisfactory color properties. On the other hand, when ratios of 20 to 1 or higher are used, a product having substantially the same color properties as before may be obtained by removing a bottom fraction of from only 0.5 to 2- per cent. These losses are far less than those encountered by the use of previously known processes. When relatively higher ratios of propane to fatty material are used, the proportion of oil absorbed is greater and the maximum temperature at the top of the tower I 2 must be established with respect to the solvent to fatty material ratio when a particular fraction of the fatty material is desired.

The temperature at the bottom of the tower must, of course, be above that temperature at which complete miscibility of the solvent and the fatty material in the lower portion of the tower occurs. The preferred bottom temperatures are generally maintained at from 5 to F. or more below the critical temperature of the solvent. When propane is employed as a solvent in the decolorization of crude fats or fatty materials, the temperature at the top of the tower may be between and 210 F., and the bottom temperature may be between 140 and 205 F.

The pressure employed in the fractionating tower I 2 is maintained sufliciently above the vapor pressure of the solvent to permit substantial variation in the tower pressure without reducing it below the vapor pressure of the solvent. A maximum operating pressure of approximately 50 pounds per square inch higher than the vapor pressure of the solvent is generally sufliciently high since adjustments of 10 to 15 pounds per square inch in the operating pressure are usually sufiicient to counteract whatever temperature variations may occur in the operation of the tower.

According to the present invention, a crude beef tallow having an initial color of 18+ (Gardner-Holt) may be reduced to a color of 34 (Gardner-Holt) by the removal of a 1 per cent bottoms when using a propane to charge material ratio of 18, and when the temperature at the top of the tower is 170 F., and the temperature at the bottom of the tower is F. The physical and chemical characteristics of the decolorized product is substantially the same as the crude fatty material since such a small proportion of this'fatty material has been removed as color bodies. However, the physical and chemical characteristics of the bottoms fraction which contains substantially all of the color bodies, differ greatly from those characteristics of the crude fatty material. It will, therefore, be seen that according to applicants invention, the decolorization of crude fats and beef tallow may be carried out far more efficiently than heretoforev by a method which is far simpler than those methods previously used and with far smaller losses than have previously been encountered. The products obtained by applicants method are particularly suitable for the manufacture of soaps, but may be used in any other industries where decolorized fatty acids and fatty materials are necessary.

We claim:

1. A continuous process for removing color bodies and oxidized fats from tallow by contacting said tallow with a solvent having a critical temperature not higher than about 450 F. which process includes the steps of continuously charging said tallow and said solvent to a vertically extended contacting zone having a solvent inlet and raffinate phase outlet near its lower end, an extract phase outlet near its upper end and a tallow inlet intermediate said ends; maintaining paracritical conditions within said contacting zone to precipitate color bodies and oxidized fats from said tallow; sampling upflowing extract phase from said zone to determine the solventoil ratio thereof; adjusting contacting zone temperature and solvent feed to maintain said ratio at a value of at least 5 parts solvent to one part oil.

2. In a continuous process for decolorizing tallow by solvent extraction under paracritical conditions with a solvent having a critical temperature not higher than about 150 F., in which tallow and solvent are charged to a vertically extended extraction zone having a propane inlet and raffinate phase outlet near the lower end, an extract phase outlet near the upper end, and a tallow charge inlet intermediate said ends, the method of controlling the quality of product in the extract phase withdrawn from said extract phase outlet which includes the steps of: maintaining in said extraction zone a precipitating zone of increasing temperature above said tallow inlet, said temperature being maintained sufiiciently high in the paracritical temperature range to precipitate a downfiowing heavy phase material from the upflowing extract phase; maintaining above said precipitating zone a settling zone of substantially constant temperature, said constant temperature being not substantially less than the maximum temperature within said precipitating zone; withdrawing upflowing extract phase from the upper end of said precipitating zone and determining the solvent-oil ratio of said withdrawn extract phase; and increasing or decreasing the quantity of downilowing reflux oil to reduce or increase solvent-oil ratio of said extract phase in a range in which said ratio is not less than 5 parts of solvent to 1 part of oil.

3. A continuous process for removing color bodies and oxidized fats from tallow by contacting said tallow with a solvent having a critical temperature not higher than about 450 F. which e process includes the steps of: continuously charging said tallow and said solvent to a vertically extended contacting zone having a solvent inlet and rafilnate phase outlet near its lower end, an extract phase outlet near its upper end and a tallow inlet intermediate said ends; maintaining paracritical conditions within said contacting zone to precipitate color bodies and oxidized fats from said tallow withdrawing extract phase from said zone by way of said extract phase outlet and at least partially dissolventizing at least part of said withdrawn extract phase to obtain a heavy phase material; and returning said heavy phase material to said contacting zone at a rate maintaining a ratio of at least 5 parts of solvent to one part of oil in said extract phase.

4. In a continuous process for decolorizing tallow by solvent extraction under paracritical conditions with a solvent having a critical temperature not higher than about 450 F., in which tallow and solvent are charged to a vertically extended extraction zone having a propane inlet and raflinate phase outlet near the lower end, an extract phase outlet near the upper end, and a tallow charge inlet intermediate said ends, the method of controlling the quality of product in the extract phase withdrawn from said extract phase outlet which includes the steps of: maintaining in said extraction zone a precipitating zone of increasing temperature above said tallow inlet, said temperature being maintained sufficiently high in the paracritical temperature range to precipitate a downflowing heavy phase material from the upflowing extract phase; maintaining above said precipitating zone a settling zone of substantially constant temperature, said constant temperature being not substantially less than the maximum temperature within said precipitating zone; collecting downfiowing heavy phase material from said constant temperature zone near the lower end thereof; withdrawing upflowing extract phase from the upper end of said constant temperature zone; and returning at least part of said collected heavy material to said extraction zone at a point below the point of collection and at a rate sufilcient to maintain a ratio of at least 5 parts of solvent to 1 part of oil in said extract phase withdrawn from said extract phase outlet.

HERBERT J. PASSINO. OLIVER MORFIT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,247,496 Hixson et a1. July 1, 1941 2,394,968 Van Orden Feb. 12, 1946 2,454,638 Dickinson et al Nov. 23, 1948 

1. A CONTINUOUS PROCESS FOR REMOVING COLOR BODIES AND OXIDIZED FATS FROM TALLOW BY CONTACTING SAID TALLOW WITH A SOLVENT HAVING A CRITICAL TEMPERATURE NOT HIGHER THAN ABOUT 450* F. WHICH PROCESS INCLUDES THE STEPS OF: CONTINUOUSLY CHARGING SAID TALLOW AND SAID SOLVENT TO A VERTICALLY EXTENDED CONTACTING ZONE HAVING A SOLVENT INLET AND RAFFINATE PHASE OUTLET NEAR ITS LOWER END, AN EXTRACT PHASE OUTLET NEAR ITS UPPER END AND A TALLOW INLET INTERMEDIATE SAID ENDS; MAINTAINING PARACRITICAL CONDITIONS WITHIN SAID CONTACTING ZONE TO PRECIPITATE COLOR BODIES AND OXIDIZED FATS FROM SAID TALLOW; SAMPLING UPFLOWING EXTRACT PHASE FROM SAID ZONE TO DETERMINE THE SOLVENTOIL RATIO THEREOF; ADJUSTING CONTACTING ZONE TEMPERATURE AND SOLVENT FEDD TO MAINTAIN SAID RATIO AT A VALUE OF AT LEAST 5 PARTS SOLVENT TO ONE PART OIL. 